Washington Atty. Gen. John Ashcroft and FBI Director Robert Mueller warned Wednesday of a possible al-Qaida attack this summer and fall in a joint statement that was part alert and part plea for public vigilance.
Ashcroft said recent intelligence "indicates al-Qaida's specific intention to hit the United States hard."
The Republican convention in Manhattan in three months and other upcoming high-profile events such as the Democratic convention in Boston in late July "may suggest especially attractive targets," Ashcroft said.
Mueller said there was a heightened threat to U.S. interests "around the world" but no indication about where or when an attack may occur.
Both men asked citizens to look out for seven people with possible ties to al-Qaida who may be plotting terrorist attacks against the United States.
Six of the names are not new -- the FBI had issued public notices on them in 2002 and 2003 -- and little was known about the seventh person, Adam Yahiye Gadahn, 25, a U.S. citizen who grew up on the West Coast and converted to Islam in his youth.
It was not known if any of the seven is in the United States, and they are not believed to be working together.
Two are among the FBI's 22 most-wanted terrorists for their alleged involvement in the bombing of two U.S. embassies in Africa in 1998. The five others are on the FBI's list of 13 people with possible terrorist ties wanted for questioning.
An FBI official said the six men and one woman were singled out because they could blend in with their English proficiency and familiarity with the United States. Two are Canadian citizens, and three lived extensively in the United States, including Gadahn and a woman who graduated from the Massachusetts Institute of Technology in 1994.
Mueller said each had "a desire and the ability to undertake planning, facilitation and attack against the United States" domestically and abroad. One of the Canadians, Amer el-Maati, is believed to have discussed hijacking a plane in Canada and flying into a building in the United States.
"We want to know whether you've seen them in your communities, heard that someone might be hiding them, have any idea where they might be," Mueller added.
The announcement perplexed some Democrats and experts, coming without an increase in the color-coded threat advisory and five weeks after Homeland Security Secretary Tom Ridge issued a similar warning about a possible al-Qaida attack before the election in November.
"It is confusing to people that the administration would indicate that al-Qaida is far along the road to planning a major attack in the United States but not raise the threat level," Sen. Charles Schumer, D-N.Y., said in a statement.
Mueller noted that he had spoken to the head of each of the FBI's 84 local offices last week, stressing the importance of increased intelligence-gathering and investigation in upcoming months. The FBI has been criticized, most recently by the Sept. 11 commission, for not adequately notifying local agents before 9-11 of heightened concern about terrorism.
An FBI official acknowledged that Wednesday's announcement was partly in response to criticism of the agency, and said it signaled a contrast to the relative secrecy about threats shortly before Sept. 11, 2001, when there was increased concern and warnings about an attack.
"We've adjusted our game plan," the official said.
Ridge, who did not attend a news conference Wednesday with Ashcroft and Mueller, said Wednesday morning on NBC "Today" there was no consensus in the administration for raising the threat level. "We don't need to raise the threat level to increase our security," Ridge said, citing increased law-enforcement activity.
Ashcroft said Wednesday that shortly after New Year's, al-Qaida announced that its preparations for an attack on the United States were 70 percent complete. After the bombing of trains in Madrid in March, al-Qaida said its arrangements for an attack in the United States were 90 percent complete, Ashcroft said.
Some experts say terrorists would target a high-profile event for maximum damage and publicity. Others say the intense security will discourage an attack and that terrorists would rather weaken the country by damaging infrastructure such as electric grids and transportation hubs.